Question: Simplify the following expression: $r = \dfrac{k}{5k} - \dfrac{-k + 9}{5k}$
Since the expressions have the same denominator we simply subtract the numerators: $r = \dfrac{k - (-k + 9)}{5k}$ Distribute the negative sign: $r = \dfrac{k + k - 9}{5k}$ Combine like terms: $r = \dfrac{2k - 9}{5k}$